1. Field of the Invention
The present invention relates in general to an oil jet device for piston cooling, and in particular to a mounting structure for a filter plug therefor.
2. Description of Background Art
Oil jet devices for cooling pistons by forcefully injecting lubricating oil to the back side of a piston have been known in the art. An example is depicted in cross section in FIG. 5.
FIG. 5 shows a crankcase 1 and a crank journal 2 rotatably supported by the crankcase 1, a plain bearing 3, a cylinder block 4 connected to the crankcase 1, and cylinder liner 5. A piston 6 capable of sliding movement is provided in the cylinder block, and the piston 6 and the crank journal 2 are connected by a con-rod 7.
The crankcase 1 has an oil passage 1a, and an oil jet member 8 is force-fit at a tip thereof.
The oil jet member 8 comprises a larger diameter portion 8a, a nozzle 8b communicating with the oil passage 1a, a smaller diameter portion 8c also serving as a filter plug, and an O-ring 9 attached on the smaller diameter portion 8c. The oil jet member 8 is mounted in the crankcase by force-fitting the smaller diameter portion 8c with the O-ring 9 attached thereon into an upper portion of the oil passage 1a from above the crankcase 1, and then abutting a lower end 5a of the cylinder liner 5 against an upper portion of the larger diameter portion 8a. 
In operation, oil is supplied to the engine from the main gallery (not shown) through an oil passage 2a in the crank journal 2 and a hole 3a formed on the plain bearing 3. From there, oil is injected from the nozzle 8b of the oil jet member 8 to the back side of the piston 6 as shown by the arrow O, thereby cooling the piston 6.
A similar oil jet device for piston cooling is disclosed in Japanese Patent Laid-Open No. 2000-87717.
One disadvantage associated with the above-described prior art device is that since the oil jet member 8 must be force-fit into the upper portion of the oil passage 1a from above the crankcase 1, a press-fitting device is required for assembly.
A device in which an oil jet member (which does not function as a filter plug) is force-fit from the crank journal side is disclosed in Japanese Patent Laid-Open No. 8408/1985, but it also requires a press-fitting device. In addition, since the smaller diameter portion 8c is force-fit into the upper portion of the oil passage 1a with the O-ring 9 fit on the smaller diameter portion 8c that serves as a filter plug, the O-ring 9 is likely to be broken in the process of force-fitting. Since the O-ring 9 is hidden from view, it cannot be checked visually, and it is impossible to tell whether the O-ring has been broken during force-fitting of the smaller diameter portion 8c into the oil passage 1a. Thus, reliability of the device may be impaired.
It is an object of the present invention to solve the aforementioned problems, and to provide an oil jet device for piston cooling in which a press-fitting device is not required, and breakage of the O-ring can be prevented.
In order to achieve the aforementioned objects, the present invention includes a device for injecting lubricating oil toward the back side of a piston comprising an oil passage opening through a crank case from a crank journal side to a side of a lower portion of the cylinder and a filter plug inserted into the oil passage from the crank journal side. The crank journal side of the oil passage is partially sealed by a plain bearing that abuts against the filter plug.
Further, the present invention includes a feed path for feeding oil to the oil passage formed by the plain bearing and the crankcase.
Additionally, the present invention includes a ring-shaped feed path for feeding oil to the oil passage formed at the bearing portion of the crankcase.
As described above, the oil jet device of the present invention injects lubricating oil toward the back side of the piston comprising an oil passage opening through the crank case from the crank journal side to the side of the lower portion of the cylinder, and a filter plug inserted into the oil passage from the crank journal side, wherein the crank journal side of the oil passage is partially sealed by a plain bearing that abuts against the filter plug. As a result, the filter plug is prevented from becoming detached because it abuts the plain bearing. Since the filter plug is inserted into the oil passage from the crank journal side and is prevented from detaching by the plain bearing, it is not necessary to employ a press-fitting device as was required in the prior art.
In addition, since the filter plug may simply be inserted into the oil passage without force-fitting, even when an O-ring is attached on the filter plug, the O-ring is very rarely broken in the course of inserting the filter plug. Consequently, reliability of the device is improved. Since the filter plug is merely inserted into the oil passage, when problems arise such as clogging in the filter plug, maintenance can be performed easily. This is accomplished simply by removing the plain bearing and detaching the filter plug. Construction of the oil passage is also vastly simplified, because in the present invention, the feed path for feeding oil into the oil passage for piston cooling is formed by the plain bearing and the crankcase.
Finally, since the feed path is formed into a ring shape at the bearing portion of the crankcase, large quantities of oil for piston cooling can be fed smoothly in comparison to prior art devices, in which oil is fed to the oil passage through the oil passage 2a in the crank journal 2. Therefore, piston cooling efficiently is greatly improved.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.